Because of the increasing cost of electrical energy the substitution of initially costlier but more energy efficient lamp types in place of incandescent lamps has become practical. A prime candidate for this substitution is the fluorescent lamp, primarily because of its high luminous efficacy.
There are many lamp holder assemblies currently available which are adapted to fit incandescent sockets and to provide both mechanical support and electrical input power for various devices including fluorescent lamp systems. Many of these assemblies, however, require alignment of the housing with respect to the incandescent fixture or portable lamp to properly clear the harp used to support a lamp shade. Exemplary of such assembles are the devices shown in U.S. Pat. No. 4,347,460 which issued to Latassa et al on Aug. 31, 1982 and U.S. Pat. No. 4,406,969 which issued to Haraden et al on Sept. 27, 1983. The former mentioned patent shows a fluorescent lamp assembly having a rectangular-shaped housing which may require alignment depending on its dimensions. The latter patent shows a lamp holder assembly having a central body with a pair of projecting arms which may interfere with replacement of the harp. To rectify this condition it is necessary to partially unscrew the assembly, which can result in a loose mechanical fit in the socket and a poor electrical connection.
U.S. Pat. No. 4,405,877, which issued to Haraden et al on Sept. 20, 1983, shows a variably positional lamp holder assembly comprised of a housing having a lower portion carrying a base fixed to the housing in a manner to allow a limited amount of rotational movement of the base relative to the lower portion. The rotational movement of the base is accomplished by providing a circumferentially extending slot formed in the lower portion and a pin fixed on the base which projects into the slot. The width of the slot, which is a determining factor in the amount of rotational movement, is limited in order to retain structural integrity of the lower portion of the housing.
Other lamp holder assemblies available on the market are provided with a base which slips in one direction, i.e., that of tightening. At some point in tightening, the torque exerted overcomes the friction of the base shell threads allowing the housing to continue to rotate while the base is firmly seated in the socket. These assemblies which allow the base to slip are sometimes not dependable because of the variation in the amount friction among different units. Too little friction results in slippage occurring too soon and thus preventing proper connection to the center electrical contact. Too much friction allows overtightening of the lamp holder assembly and may cause distortion to the female threads of the incandescent socket.